1. Field of the Invention
This invention relates to a method of making grinding stones, particularly artificial grinding stones including those in which abrasive grains are bonded to resins or metals. Throughout this specification, the term, grinding stones, means grinding, cutting, drilling, and polishing wheels, sheets, or other different shapes bonded with abrasive grains.
2. Description of the Prior Art
In the grinding operation which has been adopted from very long ago as a machining method, there remains a number of unknown factors, compared to other machining methods. To wit, the operation from selecting a grinding stone through to processing depends exclusively on the sixth sense, experience, and trial and error. Consequently, there hasn't been remarkable improvement with respect to its processing efficiency, accuracy and so on as in other machining methods. This kind of technical stagnation is due to, among other things, the fact that indefinite factors or elements associated with the employment of abrasive grinding stones in the operation as machining tools remain unsolved. Such indefinite factors are inherent in grinding stones when compared to other tools chiefly on account of the following;
(a) Grinding stones are infinitely multiple-edged tools,
(b) They are provided with randomly dispersed abrasive grains which constitute cutting edges,
(c) The shape of cutting edges or grain fractures is uneven, and
(d) They are provided with effective cutting edges which contribute to grinding, and also with ineffective edges which do not contribute to grinding (a ratio of the effective cutting edges to the ineffective edges being generally less than 10%). In addition to inherent indefiniteness caused by the above factors (a) to (d), the grinding stones undergo changes themselves with the progress of grinding operations. However, these factors have not been addressed, as mentioned above, because they do not adversely affect grinding operations very much as the operations have been generally conducted under a comparatively mild condition and mainly for finishing work in which only a small amount of metal is to be ground off, and because abrasive grinding stones are extremely inexpensive, compared to other tools. In other words, the reasons given above made those skilled in this art neglect the aforementioned indefinite factors, and have held back research and development for eliminating them.
Nevertheless, CBN grinding stones lately introduced in the middle of 1970's and the increase of employment of such super abrasive grain grinding stones along with diamond grinding stones have thrown a new light upon grinding operations. That is, since super abrasive grains have high grinding capacities, the grinding processing method by itself is also required to be highly accurate and efficient. And, since such super abrasive grains and grinding stones made of them are extremely expensive, the old way of thinking about conventional grinding stones, that is, "they wear by nature", had to be reviewed. With this trend, requirements for grinding stones, especially for super abrasive grain grinding stones shall inevitably be changed such as follows.
(a') Random factors or elements in grinding stones have to be eliminated as much as possible, so that capacities of grinding stones can be determined and changed quantitatively,
(b') Load working on each grain shall be made even, so that grinding stones can enjoy a longer life, and
(c') Ineffective cutting edges have to be eliminated as much as possible so that grinding stones can have higher efficiencies though they are inexpensive.
In order to improve efficiencies of super grain grinding stones, there have been proposed lately various kinds of techniques including those in which abrasive grains coated on their surfaces with metals are bonded to a resinous matrix. The grinding stones of this kind are not comparable to with this invention, since they are not made for eliminating the aforementioned indefinite elements or factors but mainly for improving the bonding strength of grains with the resinous matrix. It shall be noted in this connection that even when the bonding characteristics of grains with a base surface such as a resinous matrix is improved, it is hard to determine efficiencies of grinding stones at constant, to change them quantitatively, and to make super grain grinding stones less expensive by decreasing the existence of ineffective cutting edges, unless the aforementioned indefinite and random elements and factors are eliminated. A method has been known, in which abrasive grains are fixed on a base support by means of electroplating. For example, it is proposed in Japanese Patent Publication No. Sho-56-42429 to adjust the dispersion of the abrasive grains in the above kind of electroplating method by adding thereto inorganic substances such as SiO.sub.2, Al.sub.2 O.sub.3, SiC and so on which are dielectric, inert to a plating solution, of sizes substantially equal to the grains, and less hard than them. This proposed method can, however, hardly control the distribution of abrasive grains as desired, since it does not aim by its objects to eliminate the aforementioned random or indefinite factors and elements of conventional grinding stones.